1. Field of the Invention
The present invention relates to an optical information recording/reproducing apparatus for effecting recording and/or reproduction of information by utilizing a laser beam on a recording medium, and more particularly, to an optical head adapted for use in such apparatus.
2. Related Background Art
With the progress in increasing the capacity of information recording/reproducing apparatus, an optical disk memory is attracting attention as a high density recording medium. Information recording or reproduction with such an optical disk is generally conducted by radially moving an optical head with respect to the optical disk, and effecting tracking and focusing operations of a laser beam, emitted from said optical head, onto a desired track of the recording medium.
Though various methods have been proposed for moving such an optical head, a linear motor utilizing a voice coil is frequently employed for achieving high-speed access, in order to respond to the requirement of recording and retrieving data having a large capacity with a high speed. Also, for reducing the weight of the optical head itself, there has been realized an optical head of separate structure in which an objective lens and an optical path deflecting member alone are constructed as movable members while the laser light source, signal detection unit and other principal optical members are fixed on a frame member constituting a part of the apparatus.
Also, for realizing a higher response speed or a thinner structure, there is conceived a structure in which the objective lens contained in the movable unit is driven by a uniaxial actuator solely for focusing instead of a biaxial actuator for focusing and tracking, while the tracking operation is executed by the entire movable optical head.
In the following there will be given an explanation of the conventional optical information recording/reproducing apparatus (also called an optical disk apparatus) mentioned above, with reference to the attached drawings.
FIGS. 1, 2, 3 and 4 are respectively a perspective view, a plan view, a longitudinal cross-sectional view and a transversal cross-sectional view (along a line A--A in the plan view) of a conventional optical disk apparatus.
In these drawings there are shown an optical disk 1; an objective lens 2; a carriage 3 supported movably in the radial direction (arrow A) of the optical disk 1; a bobbin 4 on which the objective lens 2 is fixed; a focusing coil 5 fixed to the vertically movable bobbin 4 for focusing the objective lens 2 to the optical disk 1; paired parallel plate springs 6 respectively fixed to the bobbin 4 and the carriage 3, for supporting the bobbin 4 elastically and movably in the focusing direction (perpendicular to the plane of the drawing) with respect to the carriage 3; a driving coil 7 fixed to the carriage 3, for driving said carriage 3 in the radial direction (indicated by an arrow A) of the optical disk 1; laterally paired magnets 8 for generating a magnetic field acting on the focusing coil 5 and the driving coil 7; four guide shafts 9 fixed to the carriage 3; mutually opposed yokes 10 constituting a magnetic circuit in cooperation with the magnets 8 and also serving as a support mechanism for the carriage 3; steel balls 11 positioned between the guide shafts 9 and V-sectioned grooves 10a, 10b of the opposed yokes 10 and adapted to roll therebetween, thereby movably supporting the carriage 3 in the radial direction of the optical disk 1; rear yokes 12 supporting the magnets 8; intermediate yokes 13 connecting the opposed yokes 10 and rear yokes 12 thereby constituting a magnetic circuit; a triangular prism-shaped mirror 14, with a reflecting face 14a, for deflecting a light beam, projected parallel to the optical disk 1 from an unrepresented fixed head, into a perpendicular direction (optical axis direction of the objective lens 2), said mirror 14 being fixed, by a portion 14b thereof, to a fixing face 3a formed on the carriage 3; and a guide frame 15 serving to fix the opposed yokes 10 and rear yokes 12 thereby maintaining constant distances between said yokes and between the yokes 10.
For satisfying the optical performance required for information recording and reproduction, the objective lens employed in the optical head has to be adjusted within a precision of several minutes for the inclination of the optical axis of a light beam with respect to the optical disk constituting the information recording medium. Consequently, a precision within several minutes is required for the otical axis of the laser beam, which is projected from the fixed optical head, deflected perpendicularly to the optical disk by the triangular prism-shaped mirror and enters the objective lens.
In the above-explained conventional structure, however, since the triangular prism-shaped mirror is directly fixed on the carriage, there have been required highly precise components and an expensive and time-consuming assembling and adjusting operation in the construction of the support mechanism for the carriage, in order to attain the above-mentioned precision within several minutes.